This study sought to determine if perceived neighborhood danger impacted children's sleep. The current study asks: how does perceived neighborhood danger impact children’s sleep both quantity and quality (duration and efficiency), could children’s physical activity mediate these associations, and how do genetic and environmental factors play into these relationships? Questionnaires, biological measurements, and actigraphy watch data were collected from 709 8-year-old Arizonan twins and their parents in order to calculate neighborhood safety, sedentary physical activity, moderate to vigorous physical activity, sleep duration, and sleep efficiency as well as covariates. It was concluded that perceived neighborhood danger does not directly impact children’s sleep duration and efficiency, children’s physical activity does not mediate the relation of perceived neighborhood danger and children’s sleep, but rather, perceived neighborhood danger indirectly impacts children’s sleep duration and efficiency through moderate to vigorous activity, and finally, that both sedentary and moderate to vigorous activity are heavily influenced by genetics.